We are investigating the seasonal reproductive cycles of a number of rodents, including white footed and deer mice, cotton rats, hamsters and grasshopper mice. We seek to identify the proximate regulators of this cycle and to specify interactions of photoperiod and biological rhythms in regulation of seasonal breeding. A second major aim is to specify the neuroendocrine mediation of seasonal cycles with particular emphasis on the pineal gland and its putative hormone melatonin in transduction of environmental stimuli into altered breeding. Both behavioral and morphological-physiological indices of reproduction are recorded with attention directed toward the development of reproductive competence (puberty).